InCl(3)-catalyzed domino reaction of aromatic amines with cyclic enol ethers in water: a highly efficient synthesis of new 1,2,3,4-tetrahydroquinoline derivatives

The tetrahydroquinoline moiety is a structural feature of many natural products. By using a domino reaction of aromatic amines and cyclic enol ethers or 2-hydroxy cyclic ether catalyzed by indium chloride in water, various tetrahydroquinoline derivatives were synthesized efficiently. Most cyclization products showed cis selectivity. The use of 2,3-dihydrofuran as the cyclic enol ether provided both higher reactivity and cis selectivity than the use of 3,4-dihydro-2H-pyran. The cis selectivity was tentatively rationalized due to chelation control in water.     

Au(I)-catalyzed highly efficient intermolecular hydroamination of alkynes

[reaction: see text] Addition of aniline derivatives to aromatic and aliphatic alkynes proceeds efficiently in the presence of a gold(I) catalyst (0.01-1.0 mol %) to afford ketimines in good yields     

PdCl2-catalyzed efficient transformation of propargylic amines to (E)-alpha-chloroalkylidene-beta-lactams

[reaction: see text] The PdCl2-catalyzed cyclocarbonylation reaction of propargylic amines with CuCl2 and benzoquinone afforded (E)-alpha-chloroalkylidene-beta-lactams in moderate to good yields. The formation of the corresponding Z-isomers or five-membered products was not observed. The reaction of the readily available optically active propargylic amines provides a convenient synthesis of the corresponding (E)-alpha-chloroalkylidene-beta-lactams with high ee values. The structure and the stereochemistry of the products were established by the X-ray single-crystal diffraction study of (E)-6d and (E)-6e, which indicates that the stereoselectivity in this reaction is different from what was observed with propargylic alcohols. A rationale for this reaction was proposed.     

Copper(I)-catalyzed highly efficient synthesis of benzoselenazoles and benzotellurazoles

A simple and practical useful synthetic method of 1,3-benzoselenazoles having a heteroatom substituent such as NRR', OR, and SR groups at the 2-position was developed by the copper(I)-catalyzed reaction of 2-bromophenyl (1) or 2-iodophenyl (2) isocyanides with selenium and heteroatom nucleophiles. In addition, the synthesis of 2-amino-1,3-benzotellurazoles is also described.     

Dichloro(dodeca-2,6,10-triene-1,12-diyl)ruthenium(IV): a highly efficient catalyst for the isomerization of allylic alcohols into carbonyl compounds in organic and aqueous media

The catalytic activity of the bis(allyl)-ruthenium(iv) complex [Ru([small eta](3):[small eta](2):[small eta](3)-C(12)H(18))Cl(2)] in the transposition of allylic alcohols into carbonyl compounds, both in THF and H(2)O as solvent, is reported.     

Unusual gold(I)-catalyzed isomerization of 3-hydroxylated 1,5-enynes: highly substrate-dependent reaction manifolds

[reaction: see text] The gold(I) isomerization of diversely substituted 3-hydroxylated enynes has led to the discovery of three new unreported skeletal rearrangements furnishing structures such as alkylidene-cyclopentenes, cyclohexadienes or alpha,beta-unsaturated aldehydes under very mild conditions.     

Ruthenium(IV)-catalyzed isomerization of the C=C bond of o-allylic substrates: a theoretical and experimental study

A general mechanism to rationalize Ru(IV) -catalyzed isomerization of the C=C bond in O-allylic substrates is proposed. Calculations supporting the proposed mechanism were performed at the MPWB1K/6-311+G(d,p)+SDD level of theory. All experimental observations in different solvents (water and THF) and under different pH conditions (neutral and basic) can be interpreted in terms of the new mechanism. Theoretical analysis of the transformation from precatalyst to catalyst led to structural identification of the active species in different media. The experimentally observed induction period is related to the magnitudes of the energy barriers computed for that process. The theoretical energy profile for the catalytic cycle requires application of relatively high temperatures, as is experimentally observed. Participation of a water molecule in the reaction coordinate is mechanistically essential when the reaction is carried out in aqueous medium. The new mechanistic proposal helped to develop a new experimental procedure for isomerization of allyl ethers to 1-propenyl ethers under neutral aqueous conditions. This process is an unique example of efficient and selective catalytic isomerization of allyl ethers in aqueous medium.     

A new method for the preparation of Ru(IV) in non-complexing acid medium: Evidence for tetrameric Ru(IV)

A new method for the preparation of Ru(IV) in acid solutions is described. This method, avoiding the preparation of the highly reactive RuO₄, is based on the stoichiometric oxidation of Br^? ion of K₂RuBr₆ by BrO₃^? ion. Easy to control and reproducible the process leads to solutions of a well-known composition consisting of the tetrameric Ru(IV) ion.     

An efficient protocol for the preparation of MOM ethers and their deprotection using zirconium(IV) chloride

An efficient protocol for the preparation of MOM ethers from alcohols and formaldehyde dimethyl acetal (DMFA) using ZrCl₄ (10 mol %) at room temperature under solvent free conditions has been developed. Similarly, the same Lewis acid, ZrCl₄ (50 mol %), in isopropanol at reflux was utilised for the deprotection of MOM ethers.     

Catalyst-free alcoholysis of phosphane-boranes: a smooth, cheap, and efficient deprotection procedure

Catalyst-free alcoholytic deprotection of borane-protected phosphorus compounds offers a smooth, efficient, and clean alternative to existing deprotection methods. In this paper we report our results on the general applicability of deprotecting phosphane- and phosphite-borane adducts by means of simple alcoholysis without the use of molecular sieves as a catalyst. Phosphane-boranes bearing at least one aromatic substituent are readily deprotected in high yields. Borane complexes of trialkylphosphanes or phosphites, however, cannot be deprotected in this way. The main merit of our method is its simplicity: apart from evaporation of the solvent, no further work-up or purification is needed.     

A new polypyridyl-based Ru (II) complex as a highly efficient electrocatalyst for CO2 reduction

A new polypyridyl Ru (II) complex, cis-[Ru (Me₄phen)₂(CH₃CN)₂](NO₃)₂ (Me₄phen = 3,4,7,8-tetramethyl-1,10-phenanthroline) has been prepared and fully characterized by elemental analysis, X-ray crystallography, cyclic voltammetry and spectroscopic techniques. The solid-state structure of the complex indicated that the Ru (II) center is sitting in an N₄N′₂ coordination environment with a distorted octahedral geometry. Cyclic voltammetry technique was used to investigate the catalytic activity of the Ru (II) complex on the electrocatalytic reduction of CO₂ to CO in acetonitrile. The effect of the different reaction parameters, including the scan rate, concentration of the electrocatalyst [complex Ru (II)] and reaction temperature, on the catalytic activity was also investigated. The results showed that the electrocatalytic activity of the complex increases with increasing electrocatalyst concentration and scan rate. Further, the CO₂ reduction peak current decreases at lower temperatures owing to the inverse relationship between the temperature and activation energy. The theoretical calculations confirmed the proposed electrocatalytic mechanism comprising seven steps.     

Self-assembled layered hybrid [Ru(bpy)3]2+/manganese(III,IV) oxide: a new and efficient strategy for water oxidation

For the first time, a self-assembled layered hybrid [Ru(bpy)(3)](2+)/manganese(III,IV) as a water oxidizing system is reported.     

Boric acid: a highly efficient catalyst for transamidation of carboxamides with amines

A novel method of transamidation of carboxamides with amines using catalytic amounts of readily available boric acid under solvent-free conditions has been developed. The scope of the methodology has been demonstrated with (i) primary, secondary, and tertiary amides and phthalimide and (ii) aliphatic, aromatic, cyclic, acyclic, primary, and secondary amines.     

A highly efficient and reusable mesoporous supported Co(II) catalyst for chemoselective deprotection of aryl acetates

Chemoselective deprotection of aryl acetates is successfully carried out in excellent yield using a mesoporous silica-supported (Salen) Co(II) catalyst. The catalyst shows high thermal stability and also can be recovered and reused at least 10 times without any significant loss of its catalytic activity. The present process is environmentally benign and economical.     

Ti(IV)-based catalytic membranes for efficient and selective oxidation of secondary amines

The incorporation of homogenous Ti(IV)/trialkanolamine catalyst in polymeric membranes provided new polymeric catalytic Ti(IV)-based membranes, stable and efficient as heterogeneous catalysts for chemoselective oxidations of secondary amines to nitrones by alkyl hydroperoxides. Polyvinylidene fluoride (PVDF)-based catalytic membranes gave the best results affording products in short reaction times, high yields and selectivity using as little as 1% of catalyst, comparable with the performances of the corresponding homogeneous system. PVDF-Ti membrane could be recycled up to five runs with no loss of activity.     

Cerium(IV) sulfate tetrahydrate: a catalytic and highly chemoselective deprotection of THP,MOM, and BOM ethers

Tetrahydropyranyl (THP), methoxymethyl (MOM), and benzyloxymethyl (BOM) phenyl/alkyl ethers were efficiently cleaved to the corresponding parent hydroxyl compounds in good yields using catalytic amounts of Ce(SO₄)₂·4H₂O by microwave-assisted or conventional heating in methanol solution. Intramolecular and competitive experiments demonstrated the chemoselective deprotection of THP ethers in the presence of triisopropylsilyl (TIPS) and tert-butyldiphenylsilyl (TBDPS) phenyl ethers.     

Correspondence of Ru(III) Ru(II) and Ru(IV) Ru(III) mixed valent states in a small dinuclear complex

The diruthenium(III) compound [(μ-oxa){Ru(acac)(2)}(2)] [1, oxa(2-) =oxamidato(2-), acac(-) =2,4-pentanedionato] exhibits an S=1 ground state with antiferromagnetic spin-spin coupling (J=-40 cm(-1)). The molecular structure in the crystal of 1?2 C(7)H(8) revealed an intramolecular metal-metal distance of 5.433 ? and a notable asymmetry within the bridging ligand. Cyclic voltammetry and spectroelectrochemistry (EPR, UV/Vis/NIR) of the two-step reduction and of the two-step oxidation (irreversible second step) produced monocation and monoanion intermediates (K(c) =10(5.9)) with broad NIR absorption bands (ε ca. 2000 M(-1)cm(-1)) and maxima at 1800 (1(-)) and 1500 nm (1(+)). TD-DFT calculations support a Ru(III)Ru(II) formulation for 1(-) with a doublet ground state. The 1(+) ion (Ru(IV)Ru(III)) was calculated with an S=3/2 ground state and the doublet state higher in energy (ΔE=694.6 cm(-1)). The Mulliken spin density calculations showed little participation of the ligand bridge in the spin accommodation for all paramagnetic species [(μ-oxa){Ru(acac)(2)}(2)](n), n=+1, 0, -1, and, accordingly, the NIR absorptions were identified as metal-to-metal (intervalence) charge transfers. Whereas only one such NIR band was observed for the Ru(III)Ru(II) (4d(5)/4d(6)) system 1(-), the Ru(IV)Ru(III) (4d(4)/4d(5)) form 1(+) exhibited extended absorbance over the UV/Vis/NIR range.     

Ru(II)-catalyzed C-H bond activation for the synthesis of substituted isoquinolinium salts from benzaldehydes, amines, and alkynes

An efficient method for the synthesis of substituted isoquinolinium salts from benzaldehydes, amines, and alkynes via ruthenium-catalyzed C-H bond activation and annulation in one pot is described.     

Calcium manganese(IV) oxides: biomimetic and efficient catalysts for water oxidation

CaMnO(3) and Ca(2)Mn(3)O(8) were synthesized and characterized by SEM, XRD, FTIR and BET. Both oxides showed oxygen evolution activity in the presence of oxone, cerium(IV) ammonium nitrate and H(2)O(2). Oxygen evolution from water during irradiation with visible light (λ > 400 nm) was also observed upon adding these manganese oxides to an aqueous solution containing tris(2,2'-bipyridyl) ruthenium(II), as photosensitizer, and chloro pentaammine cobalt(III) chloride, as electron acceptor, in an acetate buffer. The amounts of dissolved manganese and calcium from CaMnO(3) and Ca(2)Mn(3)O(8) in the oxygen evolving reactions were reported and compared with other (calcium) manganese oxides. Proposed mechanisms of oxygen evolution and proposed roles for the calcium ions are also considered.     

Pd(OAc)2-catalyzed carbonylation of amines

A phosphine-free catalytic system [Pd(OAc)2-Cu(OAc)2-air] induced a substrate-specific carbonylation of amines in boiling toluene under CO gas (1 atm). Symmetrical N,N'-dialkylureas were obtained by the carbonylation of primary amines. N,N,N'-Trialkylureas were selectively formed by addition of a secondary amine to the above reaction vessel. Secondary amines did not give tetraalkylureas. However, dialkylamines with a phenyl group on their alkyl chains, such as N-monoalkylated benzylic amine or phenethylamine derivatives, underwent a direct aromatic carbonylation to afford five- or six-membered benzolactams. In the carbonylation, the chelation effect or steric repulsion between Pd(II) and the meta-substituent in the ortho-palladation and the ring sizes of cyclopalladation products that were formed prior to carbonylation were found to generate good site selectivity and increase the reaction rate. In contrast, carbonylation of omega-arylalkylamines with a hydroxyl group gave neither ureas nor benzolactams but instead produced 1,3-oxazolidinones smoothly. Hydrochlorides of amines also underwent carbonylation to afford the corresponding amides under the conditions used. This procedure made it possible to prepare ureas of amino acid esters and N-alkylcarbamates in practical yields.